Optical designs of miniaturized overlay measurement system

A sensor apparatus, comprising:

• a beam shaping system configured to shape an illumination beam generated from an illumination system and to generate a flat top beam spot of the illumination beam;
• a beam projection system configured to project the flat top beam spot toward a target on a substrate;
• and
• a signal detection system configured to collect a signal beam comprising diffraction order sub-beams generated from the target and to measure a characteristic of the target based on the collected signal beam,
• wherein the signal detection system comprises a central lens, a reflector, and a signal detector,
• wherein the central lens is a common component shared by the beam projection system and the signal detection system, and
• wherein the beam projection system comprises a field stop, a diffraction grating, two reflecting surfaces on the central lens, two concave mirrors, and a mechanical shutter.

A method for correcting a processing error of a lithographic apparatus, comprising:

• generating an illumination beam having a flat top beam spot;
• directing the flat top beam spot to a beam shaping system through:
• a collimator lens, followed by a spatial light modulator, followed by a focusing lens;
• or
• a photonic element coupled to a photonic crystal fiber, followed by a collimator lens, followed by a focusing lens;
• or
• directing the flat top beam spot through a collimator lens followed by an aspheric beam shaper;
• projecting the flat top beam spot toward a target on a substrate;
• collecting a signal beam comprising diffraction order sub-beams generated from the target;
• determining a characteristic of the target;
• and
• correcting the processing error of the lithographic apparatus based on the characteristic of the target.